This disclosure relates to polymeric compositions and methods of manufacture thereof.
Compatibilized polymeric resin blends comprising at least two polymeric resins utilized in automotive body applications such as exterior body panels, bumpers, and the like, generally possess impact properties greater than or equal to about 20 kg-cm/cm in a Notched Izod test as per ASTM D 256. In order to develop these impact properties it is desirable to adequately disperse the resins in one another as well as to disperse suitable impact modifiers throughout the bulk of the blend. Such blends have generally been manufactured on twin screw extruders having three flighted screws. These extruders are characterized by high shear rates and long residence times for the blend, which provides an adequate amount of dispersion of the impact modifier thereby improving impact properties.
Modern twin screw extruders, developed and manufactured for commercial purposes in recent years are designed to operate at higher speeds with much higher throughput rates. To achieve these high throughput rates, the number of screw flights is decreased from three to two and the channel depth is increased. This results in compounding processes wherein the average shear rates for the extruded resin are reduced when compared with the shear imparted in three flighted twin screw extruders. These reduced shear rates result in lower degrees of dispersion and mixing. It would therefore be advantageous to utilize an extruder wherein the screws are designed to operate at high speed and therefore provide high throughput, but which impart an amount of shear to the polymeric blend effective to disperse the resins as well as the impact modifier adequately, so as to advantageously obtain impact properties which permit the use of these blends in automotive applications.